The invention relates to an abrading and/or polishing machine for cereals, such as rice or,other grain varieties, comprising an abrading and or polishing rotor enclosed by a screen which consists of a plurality of screen sectors radially adjustable, which screen sectors are pivotably mounted at one respective end about a link axis.
Conventional abrading or polishing machines, in particular abrading machines, comprise an arrangement of screen sectors mounted at one circumferential end at a link axis, whereas the second circumferential end is pivotable about that axis in such a manner that it projects more or less into the space of the cereals to be treated. The purpose of this arrangement is to provide an increased resistance for the cereals carried away by the rotor toward the free end of the screen sector by an adjustment radially inwardly so that a rubbing effect is caused between the rotor and the cereals, or between the cereals, respectively. If no such resistance were to be provided, but with the screen housing being designed concentrically and circular cylindrically, the grains would be driven by the rotor to an idle circumferential motion all around the inner side of the screen, without an abrasion of husk rests and the like being produced.
When using the term "cereals" in the present patent specification, there can be meant the most diverse cereals. In general, such a treatment is carried out with rice, but at times also with other grain varieties. Furthermore, the application of such machines has already been suggested also for coffee beans.
In the design described above, axially extending flanges are located at the ends of the screen sectors, which flanges are to provide a covering when the free end of the screen sector is adjusted in radical direction, since otherwise a gap would open between the free end of the one screen sector and the linked end of the adjoining screen sector, through which gap the granular material may pass through. It is true that a complete covering will not be possible for mere geometrical reason, for in the case of a pivoting motion of one screen sector with respect to the other one, the angle of the flange relative to a radial plane extending across the link axis of the adjoining screen sector will naturally also be changed. In the case of cereals of a lower size and/or larger setting ranges, this may have the effect that a gap in between adjacent screen sector may develop, through wdhich the cereals will exit. This disadvantage also made it an essential requirement to limit the setting range of the screen sectors with the known constructions, i.e. to keep it smaller under certain conditions than would convenient.
Another drawback of the known design is caused by the fact that each single one of the primarily three, screen sectdors had to be adjusted separately, which was time consuming and led to down-times, for this work could be carried out only during times of stand-stills of the machine aftr the operator had gained acess to the screen accommodated in a housing.